Method of depositing copper using physical vapor deposition

ABSTRACT

The present method of forming an electronic structure includes providing a tantalum base layer and depositing a layer of copper on the tantalum layer, the deposition being undertaken by physical vapor deposition with the temperature of the base layer at 50.degree. C. or less, with the deposition taking place at a power level of 300 W or less.

RELATED APPLICATIONS

The present Application is a divisional of application Ser. No.11/641,647, (Attorney Docket Number SPSN-AF01925) entitled “Method ofDepositing Copper Using Physical Vapor Deposition” filed Dec. 19, 2006,which is all incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to formation of layers on asemiconductor device, and more particularly, to formation of a thincopper layer.

2. Background Art

A common technique for forming device layers of various materials is PVD(Physical Vapor Deposition). With reference to FIGS. 1 and 2, the PVDprocess is a well-known magnetron sputtering process for depositing alayer on a substrate 20 supported on a platform 21. Typically (FIG. 1),a target 22 of the desired layer material is provided inside a vacuumchamber 24, and argon gas is introduced into the chamber 24 and isionized to a positive charge (26). The target 22 is held at negative,while the wall of the chamber 24 is grounded, so that DC power isapplied to add energy to the argon gas ions 26, causing the ions 26 tobe accelerated toward the target 22. During the acceleration, the ions26 gain momentum and strike the target 22. This causes atoms ormolecules 28 of the target 22 to scatter in the chamber 24, with somebeing deposited on the substrate 20.

Formation of a thin (for example 20 angstroms thick), continuous copperlayer on an oxide layer of a wafer using a copper target 29) has provenproblematical. When using conventional PVD processes to form such a thincopper layer (containing only a small amount of copper) on an oxide suchas SiO.sub.2 30, high surface tension causes the copper to form in largeseparate grains/crystals during the initial deposition, to minimizesurface energy (so-called island growth). This island growth causes thedeposited copper to agglomerate into distinct, separate copper globules32 (FIG. 2) rather than a smooth, continuous, uniform layer as isdesired.

What is needed is an approach wherein a smooth, continuous, uniform,thin copper layer may be formed.

DISCLOSURE OF THE INVENTION

Broadly stated, the present method of forming an electronic structurecomprises providing a base layer and depositing a layer of copper byphysical vapor deposition with the temperature of the base layer at50.degree. C. or less, with the deposition taking place at a power levelof 300 W or less.

The present invention is better understood upon consideration of thedetailed description below, in conjunction with the accompanyingdrawings. As will become readily apparent to those skilled in the artfrom the following description, there is shown and described anembodiment of this invention simply by way of the illustration of thebest mode to carry out the invention. As will be realized, the inventionis capable of other embodiments and its several details are capable ofmodifications and various obvious aspects, all without departing fromthe scope of the invention. Accordingly, the drawings and detaileddescription will be regarded as illustrative in nature and not asrestrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well assaid preferred mode of use, and further objects and advantages thereof,will best be understood by reference to the following detaileddescription of an illustrative embodiment when read in conjunction withthe accompanying drawings, wherein:

FIGS. 1 and 2 illustrate a typical prior approach in using PVD todeposit copper;

FIG. 3-8 illustrate the present approach in using PVD to deposit copper;and

FIG. 9-11 are systems incorporating devices formed using the presentmethod.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Reference is now made in detail to a specific embodiment of the presentinvention which illustrates the best mode presently contemplated by theinventors for practicing the invention.

In the present approach, in forming an electronic structure, prior tothe formation of a copper layer, a base layer of tantalum 40 isdeposited on an oxide layer, for example an SiO.sub.2 layer 42 of awafer 44 on platform 45 (FIG. 3). This process is undertaken in adeposition chamber 46 (internal temperature approximately 30.degree. C.)using conventional DC magnetron PVD techniques. That is, a target 48 oftantalum is provided inside chamber 46, and argon gas is introduced intothe chamber 46 and is ionized to a positive charge (50). The target 48is held at negative, while the wall of the chamber 46 is grounded, sothat DC power is applied to add energy to the argon gas ions 50, causingthe ions 50 to be accelerated toward the target 48. During theacceleration, the ions 50 gain momentum and strike the target 48. Thiscauses tantalum atoms 52 of the target 48 to scatter in the chamber 46,with some being deposited on the oxide layer 42 of the wafer 44 to formtantalum layer 40. The striking of the tantalum target material 48 withargon ions 50 causes the tantalum target material 48 to greatly increasein temperature, causing the temperature of the deposited tantalum layer40 to be at a greatly elevated temperature (for example 200.degree. C.).

The resulting wafer 44 with tantalum 40 thereon, which is at the abovedescribed elevated temperature of approximately 200.degree. C., isimmediately transferred to another DC magnetron sputtering chamber 54,so as to avoid contamination (FIG. 4), placed on platform 55 therein(internal temperature of chamber 54 approximately 30.degree. C.) forformation of a thin copper layer on the tantalum layer 40, by means of acopper target 56 as will be shown and described.

Immediately after the wafer 44 with tantalum layer 40 thereon enters thechamber 54, a pumpdown step is undertaken to provide a vacuum in thechamber 54 (FIG. 5). This step takes only a short time (in this example3 seconds) and so the temperature of the tantalum layer 40 remains near200.degree. C.

After this step is completed, a cooling step is undertaken, with argongas flowing (FIG. 6), but without DC power. This step is undertaken foran extended period of time, in this embodiment 60 seconds, with argongas flowing to the backside of the wafer 44 to effectively cool down thewafer 44 and tantalum layer 40. so that the tantalum layer 40 cools downto 50.degree. C. or less, preferably to approximately 30.degree. C., theinternal temperature of the chamber 54.

After this step is completed, a deposition step is undertaken (FIG. 7),with low DC power applied (300 w or less, in this embodiment 200 W).Argon gas continues to be introduced into the chamber 54 to establish apressure of approximately 5 mTorr, and is ionized to a positive charge(58). The pressure and DC power level are carefully selected in order toobtain a stable plasma. The target 56 is held at negative, while thewall of the chamber 54 is grounded, so that DC power is applied to addenergy to the argon gas ions 58, causing the ions 58 to be acceleratedtoward the target 56. During the acceleration, the ions 58 gain momentumand strike the copper target 56. This causes atoms 60 of copper toscatter in the chamber 54, with some being deposited on the tantalumlayer 40. This deposition step is undertaken in this example for 10seconds.

The tantalum layer 40 at low temperature promotes smooth coppernucleation across the surface of the tantalum layer 40, avoiding theisland growth described above. In addition, the low temperature of thetantalum layer 40 along with low power applied during the depositionstep (for example 200 W rather than for example 800 W or more aspreviously applied) promotes formation of a smooth, continuous, uniform,thin copper layer 62 (30 angstroms or less, in this embodimentapproximately 20 angstroms) on the tantalum layer 40 by avoidingformation of globules thereof as described thereof.

Finally, another pump-down step is undertaken (FIG. 8).

The present method succeeds in forming a thin, uniform smooth,continuous copper layer 62.

FIG. 9 illustrates a system 200 utilizing devices formed using themethod described above. As shown therein, the system 200 includeshand-held devices in the form of cell phones 202, which communicatethrough an intermediate apparatus such as a tower 204 (shown) and/or asatellite. Signals are provided from one cell phone to the other throughthe tower 204. Such a cell phone 202 with advantage uses devices formedas shown and described. One skilled in the art will readily understandthe advantage of using such devices in other hand-held devices whichutilize data storage, such as portable media players, personal digitalassistants, digital cameras and the like.

FIG. 10 illustrates another system 300 utilizing devices formed usingthe method described above. The system 300 includes a vehicle 302 havingan engine 304 controlled by an electronic control unit 306. Theelectronic control unit 306 with advantage uses such devices.

FIG. 11 illustrates yet another system 400 utilizing devices formedusing the method described above. This system 400 is a computer 402which includes an input in the form of a keyboard, and a microprocessorfor receiving signals from the keyboard through an interface. Themicroprocessor also communicates with a CDROM drive, a hard drive, and afloppy drive through interfaces. Output from the microprocessor isprovided to a monitor through an interface. Also connected to andcommunicating with the microprocessor is memory which may take the formof ROM, RAM, flash and/or other forms of memory. The system withadvantage uses such devices.

The foregoing description of the embodiment of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Other modifications or variations are possible in light ofthe above teachings.

The embodiment was chosen and described to provide the best illustrationof the principles of the invention and its practical application tothereby enable one of ordinary skill of the art to utilize the inventionin various embodiments and with various modifications as are suited tothe particular use contemplated. All such modifications and variationsare within the scope of the invention as determined by the appendedclaims when interpreted in accordance with the breadth to which they arefairly, legally and equitably entitled.

What is claimed is:
 1. A method of forming an electronic structurecomprising: providing a base layer; and depositing a layer of copper onthe base layer by physical vapor deposition at a power level of 300 W orless.
 2. The method of claim 1, wherein the base layer comprisestantalum.
 3. The method of claim 1, wherein the base layer is formed ona layer of oxide that is formed on the surface of a wafer.
 4. The methodof claim 3, wherein the wafer with the layer of oxide and the base layerare transformed to a chamber, after forming the base layer, to avoidcontamination.
 5. The method of claim 4, further comprising a pump-downstep to provide the vacuum.
 6. The method of claim 5, wherein thepump-down step takes a short time of approximately 3 seconds.
 7. Themethod of claim 1, further comprising rapid cooling of the layer ofoxide and the base layer.
 8. The method of claim 7, wherein rapidcooling is done using a gas flow without a DC power.
 9. The method ofclaim 7, wherein rapid cooling is performed for an extended period oftime.
 10. The method of claim 1, wherein the power level of 300 W orless and a cool base layer promote a smooth, continuous, uniform, andthin formation of the layer of copper.
 11. The method of claim 1,wherein said electronic structure is incorporated in a system.
 12. Themethod of claim 1, wherein the system is selected from the groupconsisting of a vehicle, and a hand-held device.
 13. The method of claim1, wherein a pressure and the power level are selected, for depositingthe layer of copper, in order to obtain a stable plasma.
 14. A method offorming an electronic structure incorporated in a computer system, saidmethod comprising: providing a base layer on a layer of oxide that isformed on the surface of a wafer; and depositing a layer of copper onthe base layer by physical vapor deposition at a power level of 300 W orless.
 15. The method of claim 14, wherein the wafer with the layer ofoxide and the base layer are transformed to a chamber, after forming thebase layer, to avoid contamination and to provide a vacuum.
 16. Themethod of claim 15, further comprising a pump-down step to provide thevacuum.
 17. The method of claim 14, further comprising rapid cooling ofthe layer of oxide and the base layer.
 18. The method of claim 14,wherein the power level of 300 W or less and a cool base layer promote asmooth, continuous, uniform, and thin formation of the layer of copper.19. The method of claim 2, wherein the rapid cooling is performed afterforming of the tantalum layer.
 20. The method of claim 9, wherein theextended period of time is approximately 60 seconds.